What can I do for my Rosemary plant?

I’ve never had a green thumb. Nevertheless, I got a rosemary plant not too long ago, and I put it in a pot. I got some dirt that has plant food in it. I’ve watered it about every day and keep it on the outside windowsill that gets the most sunlight. It has slowly been dying, drying out. Am I over-watering it? Under-watering? Wrong soil? Too much sun? Not enough sun? What can I do to help it?